1. Field of the Invention
The present invention relates to a lens driving device using an oscillation wave motor.
2. Description of the Prior Art
When an oscillation wave motor with electrorestriction elements is used for a lens driving, the device can be simplified and made compact, but certain problems will arise. That is, since the oscillation wave motor has an oscillator and a moving element pressed against each other and uses the frictional force generated therefrom as a driving transmission source as will be described below, a great amount of force overcoming said frictional force will be needed in order to move a rotation ring for a rotor which is a moving element at the time of a manual (driving) operation. Thus, a torque greater than a frictional torque will be needed at the time of a manual operation for lens driving, and it has been necessary to reduce the torque for securing better operating characteristics. Also, while there is known a method which operates to place the oscillation of an oscillation ring for a stator as an oscillator in a stationary wave state for reducing the contacting area between the oscillation ring for the stator and a rotation ring for the rotor, thus reducing the friction torque, it will be necessary in such a method to supply power to the electrorestriction elements even at the time of a manual operation. This results in a problem increasing the power consumption which requires a power source with a greater capacity. Further, there could be utilized a method which operates to provide a clutch mechanism to secure pressure contact and separation of the oscillation ring for a stator and the rotation ring for a rotor, but when merely a clutch mechanism alone is provided, when the coupling is released by the clutch the rotation ring for the rotor which operates as a moving element will have too small a rotation load, and, therefore, a problem will arise causing difficulty in retaining the rotation of the same at a desired position.